In micro-processing for manufacturing a semiconductor device or a FPD (Flat Panel Display) using plasma, it is very important to control a temperature or a temperature distribution of a processing target substrate (a semiconductor wafer, a glass substrate, etc.) as well as to control a plasma density distribution on the processing target substrate. If the temperature control of the substrate is not properly performed, not only the uniformity of a surface reaction of the substrate but also the uniformity of process characteristics may not be achieved, so that a production yield of semiconductor devices or display devices is decreased.
In general, a mounting table or susceptor, which mounts thereon a processing target substrate within a chamber of a plasma processing apparatus (particularly, a capacitively coupled plasma processing apparatus), has a function as a high frequency electrode that applies a high frequency power into a plasma space, a function as a holder that holds thereon the substrate by electrostatic attraction or the like, and a function as a temperature controller that controls the temperature of the substrate to a preset temperature through heat transfer. As for the temperature control function, it is required to appropriately correct a heat input characteristic distribution of the substrate affected by non-uniform radiant heat from plasma or a wall of the chamber, or a heat distribution affected by a substrate supporting structure.
Conventionally, in order to control the temperature of the susceptor and, further, the temperature of the substrate, a heater structure is widely employed. In this heater structure, a heating element that generates heat by an electric current applied thereto is provided in the susceptor, and Joule heat generated by the heating element is controlled. When using this heater structure, however, a part of a high frequency power applied to the susceptor from a high frequency power supply may be easily introduced into a heater power feed line through the heating element as a noise. If this high frequency noise reaches a heater power supply through the heater power feed line, operation and performance of the heater power supply is degraded. Furthermore, if a high frequency current flows in the heater power feed line, the high frequency power may be wasted. Typically, to solve these problems, a filter that reduces or blocks the high frequency noise flowing from the heating element embedded in the susceptor is provided on the heater power feed line.
The present applicant describes, in Patent Document 1, a filter technique that provides improved stability and reproducibility of filter performance for blocking a high frequency noise introduced to a line such as a power feed line or a signal line from an electrical member other than a high frequency electrode within a processing vessel of a plasma processing apparatus. This filter technique employs a regular multiple parallel resonance characteristic of a distributed constant line. Accordingly, only one air core coil is provided, and, also, stable noise blocking characteristic less affected by the apparatus difference can be obtained.
Further, the present applicant also describes, in Patent Document 1, a technique of a parallel resonance frequency adjuster capable of controlling at least one of multiple parallel resonance frequencies by locally changing characteristic impedance of the distributed constant line by way of, for example, coaxially providing a conductive ring member between the air core coil and an external conductor. Since at least one of the multiple parallel resonance frequencies can be set to be equal to or approximate to a frequency of a high frequency noise to be blocked, sufficiently high impedance as required can be applied to the frequency of this high frequency noise by the parallel resonance frequency adjuster. Thus, the heater power supply can be protected securely, and reproducibility and reliability of the plasma process can be improved.
Patent Document 1: Japanese Patent Laid-open Publication No. 2011-135052
However, in the prior art described in Patent Document 1, since a distance between the coil and the external conductor is locally narrowed at the position where the ring member is provided, an impedance function and a withstanding voltage characteristic of the coil against the high frequency noise are degraded. That is, a potential of a high frequency power on the heater power feed line is as high (e.g., several thousands of volts) as a surface potential of a power feed rod or the susceptor (lower high frequency electrode) at an inlet portion of a filter unit. Further, the potential of the high frequency power decreases gradually in an axial direction along a winding of the coil within the filter unit, and becomes several tens of volts at a termination end of the coil. If the ring member as mentioned above is provided, however, the high frequency noise flows to the ground on the way down the coil while bypassing an air gap and the ring member provided outwardly in a radial direction. As a result, the impedance function of the filter unit against the high frequency noise cannot be sufficiently exerted, and damage or early degradation of components (coil conductor, coil tube, ring member, etc.) in the vicinity of a bypass in which the high current flows may easily occur.
In the plasma processing apparatus using the high frequency power for the plasma process, various transmission circuits such as a matching unit, a filter circuit and a connecting circuit are provided on a line that electrically connects the high frequency power supply provided at the outside of the chamber and the electrode provided at the inside or in the vicinity of the chamber. In such a case, if a relatively short air core coil serving as a lumped constant element is used as a coil included in the transmission circuit, a parallel LC circuit may be formed between self-inductance of the air core coil and a parasitic capacitance in the vicinity of the air core coil, so that self-resonance may easily occur. From one point of view, such self-resonance characteristic of the air core coil may block an undesired high frequency power, for example, a harmonic wave on the line.
In such a case, the air core coil needs to have preset self-inductance required within the transmission circuit and, also, a self-resonance frequency close to a frequency of the harmonic wave to be blocked. Typically, the self-inductance, which is determined uniquely by a diameter, a length and a winding number of the coil itself, is the main condition that the air core coil needs to satisfy. Meanwhile, since the self-resonance frequency depends on a parasitic capacitance of the air core coil, i.e., a capacitance between coil wires or between a stray capacitance generated between the coil and an adjacent conductor such as a housing, the self-resonance frequency can be adjusted from this aspect. That is, the vicinity of the air core coil needs to be designed such that a parasitic capacitance (capacitance between the coil wires, stray capacitance) that applies the required self-resonance frequency is formed under the required self-inductance. Actually, however, there exists non-uniformity or variation in the winding structure of the air core coil on the manufacturing level, and, currently, there is proposed no effective way to adjust the self-resonance frequency in the vicinity of the air core coil.